The present invention relates to piezoelectric sonic transducers and more particularly to a buzzer in which the piezoelectric element is mounted on a metallic plate which acts as an electrode and which includes a plurality of integrally formed supporting struts. It has been known to use a piezoelectric device, such as a lead zirconate crystal, to change electrical energy into mechanical energy in the form of sound. It is known that if an electrical potential is placed across such a crystal, the crystal will deform in shape. If the potential is then removed, the crystal will return to its original configuration. Application of an alternating voltage of appropriate frequency to such a crystal results in rapid vibration of the crystal and consequently the emission of sound waves. The use of such a piezoelectric device in a buzzer is advantageous in that no adjustment is needed and the sparking which is characteristic of electromagnetic buzzers is eliminated.
Various approaches have been taken to mount a sonic transducer crystal in a buzzer. U.S. Pat. No. 2,831,989 to Ianouchevsky, issued Apr. 22, 1958, discloses a support for a crystal which includes three support members spaced around a crystal disc at points on the nodal plane of the disc. At such nodal points, the flexure of the crystal disc will be minimized and the support mechanisms will therefore not be subjected to intense vibration.
U.S. Pat. No. 3,263,103 to Frazier et al., issued July 26, 1966, discloses a crystal mount in which leads to the crystal electrodes also serve as support members for the crystal. Similarly U.S. Pat. No. 3,085,167 to Kritz, issued Apr. 9, 1963, and U.S. Pat. No. 3,114,848 issued Dec. 17, 1963, to Kritz show a sonic transducer in which the support members are equidistantly spaced around a piezoelectric disc on the nodal circle of the disc. One or all of the support members may be electrically connected to the exciting oscillator circuit.
U.S. Pat. No. 3,022,431 to McKnight, issued Feb. 20, 1962, shows a manner of crystal support in which two supports are each electrically connected to one of two opposing electrodes on a piezoelectric crystal, thus avoiding the necessity of providing separate electrode contacting wires.
U.S. Pat. No. 3,331,970 to Dundon et al., issued July 18, 1967, shows a method of transducer support in which clips are arranged around the periphery of the transducer assembly to grasp the transducer.
U.S. Pat. No. 3,857,146 to Engdahl shows a suspension for a quartz rod where the supporting members are formed form a single sheet of metal to provide a rugged and easily fabricated support member.
As shown in U.S. Pat. No. 3,277,466 to Potter, issued Oct. 4, 1966, it is also known to use a transducer having an electrode providing a feedback signal to the oscillator circuit which indicates that flexure has occurred. In the manner, the oscillator circuit causes the piezoelectric device to oscillate at the natural frequency of the transducer.